As an alternative to vascular surgery, balloon angioplasty has become a common method for unblocking narrowed or occluded blood vessels. In this procedure, an angioplasty balloon is inflated within a stenosed vessel in order to dilate the vessel to provide an enlarged lumen. Although balloon angioplasty has been successful in restoring flow in stenotic or occluded vessels, these vessels often restenose due to excessive neointima formation, inward vessel remodeling, and elastic recoil of the diseased tissue. It has been determined that restenosis after coronary balloon angioplasty requires additional treatment in about 35-40% of treated lesions. Although various pharmacological, mechanical, and radiological methods have been utilized, the rate of restenosis has continued to be unacceptably high.
Recently, it was shown in a porcine model that post angioplasty irradiation of the vessel effectively reduced the restenotic response following an experimentally induced coronary overstretch lesion. The attention to date has been focused on gamma ray (e.g., .sup.192 Ir and .sup.125 I) and beta particle (e.g., .sup.32 p, .sup.89 Sr-.sup.90 Y, and .sup.131 I) emitting radioisotopes. The relatively long half-lives of those species mean that the species can be conveniently produced off-site and then transported to the particular institution where the treatment is to occur.
One approach for treating a vessel with radiation to prevent restenosis has been to use radioactive materials in solid form, such as radioactive seeds, coils, or wires. The radioactive materials are enclosed by a catheter and, accordingly, do not come in contact with the patient's blood, thereby eliminating the risk of inadvertently releasing the radioactive material into the patient's blood stream. When gamma ray and beta particle emitters are used, the radiotoxicity associated with direct contact between the radioactive material and the patient's blood stream stems from the very long physical half-lives of these species, as well as from the fact that these emitters tend to accumulate in critical organs like the bone marrow. Further, the use of radioactive materials in solid, as opposed to liquid, form minimizes the shut-down period required to adequately decontaminate a laboratory in the event that the radioactive material escapes from the catheter. However, the radiation source in the proposed devices is difficult to center within the body structure being treated. Accurate centering of the radiation source is required to insure equal dosing along the length and circumference of the body structure being treated. Accordingly, such devices suffer from the disadvantage of over dosing some sections of the body structure being treated and under dosing other sections.
A second approach has been to use a radiation source in liquid form wherein the liquid is contained within an angioplasty balloon positioned within the body structure being treated. However, a rupture of the balloon would release the radioactive liquid directly into the patient's blood stream. Since balloon failure is believed to occur in about 0.1% of cases, special precautions must be taken to minimize the risk of whole-body exposure in the event of a balloon rupture. Towards that end, the use of balloon catheters with multiple wall layers has been proposed. In these devices, a second wall layer would contain the radioisotope in case one layer ruptured. However, these devices have a complicated structure, are expensive to manufacture, and have thicker front profiles making them more difficult to handle.
In light of the foregoing, it would be highly advantageous to provide a system and method for treating a body structure with radiation wherein the system and method minimize the risk of whole-body exposure to radiation under all circumstances for both the patient and the staff. Towards that end, the system and method preferably utilizes a radioactive material having a relatively short half-life (e.g., less than about 2 days). Preferably, the system should comprise means for cheaply and conveniently producing the radiation as close to the time of use as is practical. In addition, the system should be able to provide a therapeutic dose of radiation uniformly along the entire length and circumference of the body structure being treated in a reasonable amount of time (e.g., about 2-5 minutes). Further, the system should provide means for safely and easily handling the radioactive material, dosing the patient, and disposing of the radioactive material.